1. Field of the Invention
The present invention relates to a heat transferable label and improved release composition therefor.
2. Description of the Prior Art
Prior art heat transferable labels for imprinting designs onto an article typically involve decorative laminates consisting of a paper base sheet or web coated with a wax or polymeric release layer over which a design is imprinted in ink.
U.S. Pat. No. 3,616,015 is illustrative of the prior art. In U.S. Pat. No. 3,616,015 a label-carrying web such as a paper sheet includes a heat transferable label composed of a wax release layer affixed to a surface of the paper sheet and an ink design layer superimposed onto the wax release layer. In the heat transfer labelling process for imprinting designs onto articles, the label-carrying web is subjected to heat, and the laminate is pressed onto an article with the ink design layer making direct contact with the article. As the web or paper sheet is subjected to heat, the wax layer begins to melt so that the paper sheet can be released from the wax layer. After transfer of the design to the article, the paper sheet is immediately removed, leaving the design firmly affixed to the surface with the wax layer exposed to the environment. The wax release layer should not only permit release of the transferable label from the web upon application of heat to the web but also form a clear, protective layer over the transferred ink design.
This commonly assigned patent discloses a wax release coating containing a modified montan wax which has been oxidized, esterfied, and partially saponified. Paraffin wax, microcrystalline wax, and a rosin ester are included in the wax blend along with the montan wax. In order to attain improved clarity of the transferred ink design, the transferred wax coating over the ink design is subjected to additional heat processing after the label has been transferred onto an article. The additional processing involves postflaming, wherein the transferred wax coating is subjected to jets of high temperature gas either as direct gas flame or as hot air jets at temperatures of about 300.degree. F. to 400.degree. F. for a period of time sufficient to remelt the wax coating without substantially heating the bottle. Upon cooling of the remelted wax coating through use of ambient or forced cooled air, the cooled wax layer solidifies to form a clear, smooth, glossy, protective coating over the transferred ink design. Since the release coating disclosed in this reference produces a glossy, protective coating over the transferred ink design, the release composition disclosed therein is not suitable when the transferred image is desired to have a nonglossy, matte appearance. Also, the release disclosed in U.S. Pat. No. 3,616,015 may exhibit a degree of hazing noticeable over the transferred label when the transfer is made onto clear plastic materials. U.S. Pat. No. 3,616,015 is herein incorporated by reference.
U.S. Pat. No. 3,516,842 discloses a heat transfer label which is heat transferable from a paper carrier sheet to a plastic bottle. This reference discloses a wax-like release layer which may be composed of any one of three compositions: (I) the release disclosed may be composed of a slightly oxidized, low molecular weight polyethylene wax (col. 2, line 65 to col. 3, line 3); or (II) the release layer may be of an unoxidized hard wax, which wax after deposition on the paper carrier has been subjected to corona discharge (col. 3, lines 4-13); or (III) the release layer may be a blend of ethylenevinylacetate (EVA) copolymer and a paraffin wax (col. 3, lines 14-21). These release compositions do not provide sufficient adhesive properties to uniformly bond the ink design layer or intermediate lacquer coating which may be included between the release layer and ink design layer. The above release compositions do not exhibit the required high degree of film integrity during the heat transfer of the print image to the receiving article. Lack of sufficient film integrity results in shrinkage of the release layer during transfer and distortion of the transferred image.
U.S. Pat. No. 2,989,413 discloses a heat transferable laminate employing a release layer composed of an unoxidized Fisher-Tropsch wax. The unoxidized wax is employed as a release layer without incorporation of other wax or resin additive. The use of unoxidized waxes alone in release coatings for heat transferable laminates has proved to be unsatisfactory. Ink is apt to migrate into the wax upon printing and part of the ink layer may split on transfer. Also, unoxidized wax alone does not exhibit sufficient adhesive properties to uniformly bond the ink design or intermediate lacquer coating to the release surface.
U.S. Pat. No. 2,990,311 discloses a heat transferable decal having a release transfer layer composed of a mixture of a crystalline wax and a synthetic thermoplastic film-forming resin, principally an organic linear thermoplastic film-forming resin which is substantially water insoluble. The degree of compatibility of the resin and wax is controlled through selection and ratio of the components to give heat transfers of either the hot-peel or cold-peel type. In the hot-peel transfer, the decal will adhere and release from the backing only immediately after application while the decal is still hot. In the cold-peel transfer, the transferred decal will adhere to the receiving surface when hot but will only release and transfer by peeling away the backing after the transfer has cooled. In either type of transfer, this reference teaches that resins and waxes (the latter being used for the release layer) should be mutually incompatible or insoluble at temperatures below the melting temperature of the wax such that the molten wax, upon cooling, will actually crystallize separately and distinctly from the resin.
Suitable resins specifically disclosed are polyvinyl acetate, polyethyl acrylate, polymethyl acrylate, polyethyl methacrylate, polypropyl methacrylate, polybutyl methacrylate, styrenebutadiene, acrylonitrile-butadiene, polychloroprene rubbers, polyvinyl butyral, ethyl cellulose, and polyvinyl acetate vinyl stearate copolymer (col. 5, lines 38-44). The reference teaches that the wax component should be a material which derives its crystallinity mainly from the presence of long hydrocarbon chains, and should melt over a relatively narrow range between the temperatures of about 50.degree. C. to 110.degree. C. The penetrometer hardness value (ASTM D5-52) when tested with 100 grams for 5 seconds at 28.degree. C. should be below about 15. Specific waxes disclosed as suitable are beeswax, candelilla wax, carnauba wax, hydrogenated castor oil, montan wax, paraffin wax, low molecular weight polyethylene, oxidized microcrystalline wax, and hard wax or derivatives thereof obtained from the Fischer Tropsch synthesis. (col. 5, lines 45-56). This reference does not disclose applicant's formulation for the release layer nor does it contemplate the advantages which applicant has derived from such formulation.
U.S. Pat. No. 2,862,832 discloses a heat transferable decal having a release layer composed of an oxidized wax. The disclosure is directed principally to defining the type of wax found to provide suitable release of the decal from the carrier web upon application of heat. The wax disclosed in this reference is an oxidized wax obtained as the reaction product of the oxidation of hard, high melting, aliphatic, hydrocarbon waxes. The oxidized waxes are defined as the oxidation products of both natural and synthetic hydrocarbon waxes such as petroleum waxes, low molecular weight polyethylene and waxes obtained from the Fischer-Tropsch synthesis. Suitable waxes may include oxidized microcrystalline wax or the esterification product of an oxidized hydrocarbon wax. The oxidized waxes are disclosed as those having melting points between about 50.degree. C. and 110.degree. C., saponification values between about 25 and 100, acid values between about 5 and 40, and penetrometer hardness (ASTM D5-52) below about 51 as measured with 100 grams for 5 seconds at 25.degree. C. This reference does not disclose applicant's release formulation nor does it recognize or contemplate the advantages obtained from such formulation.
U.S. Pat. No. 3,616,176 discloses a heat transfer laminate of a type related to that disclosed in U.S. Pat. No. 3,616,015. In U.S. Pat. No. 3,616,176 the laminate is composed of a base sheet, with a polyamide layer covering the base sheet and a decorative ink layer covering the polyamide layer. Sufficient heat is applied to the laminate to heat the polyamide layer at or above a softening point, and the laminate is then pressed onto the surface of an article with the decorative ink layer coming into direct contact. Upon withdrawal of the heat source, the polyamide layer cools to a temperature below the softening point and the base sheet is removed. The decorative layer becomes fused or heat sealed to the article. The polyamide layer in this disclosure functions as a release coating which allows transfer of the decorative layer onto an article and upon cooling serves as a protective coating layer over the transferred decorative layer. The use of a polyamide release coating has the principal disadvantage in that there is a significant tendency for the polyamide to form a noticeable halo around the transferred decorative layer. Also, the polyamide layer even when subjected to additional processing such as post-flaming does not form a sufficiently clear coating that would aesthetically permit heat transfer labelling onto clear articles or bottles.
Accordingly, it is an object of the present invention to provide an improved release for heat transferable substrates which permits transfer of an ink design image from a support member to an article, such as a plastic bottle, and produces a nonglossy protective coating over the transferred ink design image.
It is an important object of the invention to provide an improved release for heat transferable substrates wherein the release exhibits improved anchorage for the ink design layer without sacrifice in release properties during heat transfer.
It is another object to provide an improved release which effects heat transfer of an ink design image to an article without distorting the image during transfer.